1. Field of the Invention
The present invention relates to a mineral composition containing a mixed solid phase of calcium and magnesium carbonates, to a method for preparing the same and the use thereof.
2. Description of the Prior Art
Synthetic calcium carbonates are known, chiefly for uses as fillers (paper, paint, plastics). For these applications it is particularly known to synthesise dense carbonates, in particular calcite which is of scalenohedral, rhombohedral or prismatic morphology, or aragonite having acicular morphology.
Compositions are also known containing synthetic calcium and magnesium carbonates which are notably used in the field of paper and plastic material manufacture.
For example compositions according to patent applications EP-A-2322581 and DE-A-3245103 can be cited. The first discloses plate-like magnesium carbonate particles in the form of hydromagnesite in a mixture with colloidal calcium carbonate, well suited as fillers for paper or plastic materials. The second discloses scalenohedral calcium carbonate particles (i.e. in rice grain form) in a mixture with plate-like particles of basic magnesium carbonate. The respective carbonates are produced separately and do not form a composite.
The compositions described in European patent EP-B-0526121 are formed of a uniform mixture of calcium carbonate particles having a crystalline structure of acicular aragonite with columnar particle configuration and of hydrated magnesium carbonate having a plate-like particle configuration.
Japanese patent application JP 63-123810 is also known which describes a method for producing a mineral composition containing a mixed solid phase of calcium and magnesium carbonates. This method comprises carbonation of an aqueous suspension of basic magnesium carbonate to which is continuously added an aqueous suspension of magnesium hydroxide and calcium hydroxide. Carbonation is conducted with high CO2 flow rate which gives rise to the formation of spherical, porous particles of basic magnesium carbonate on the germination nuclei of the basic magnesium carbonate initially present in suspension, the pores of these particles being partly filled with calcium carbonate. This composition is highly dense and intended for the production of fillers in the field of paper, paint, plastic material manufacture or for the medical sector.